1. Field of the Invention
This invention relates to a capsule type endoscope, and in particular, to a capsule type endoscope used to examine the part of a cylindrical structure such as the small intestine.
2. Description of Related Art
Recently, in endoscopy, capsule type endoscopes have come to be used in the field of medicine. Such an endoscope does not require an insertion tube, is provided with a transparent cover at its distal end, and is configured into a capsule shape so that when a patient swallows the capsule type endoscope, pain that formerly has been experienced by the insertion of the insertion tube section can be relieved.
In a common endoscope, for example, in order to form images inside the stomach in a wide range and to search a lesion, an illumination optical system is constructed so that the region of a visual field to be imaged is made wide as far as possible, an illumination region of illumination light illuminating this region to be imaged is made large as far as possible, and the illuminance of the entire imaging area becomes uniform. Such wide-angle illumination optical systems are disclosed, for example, in Japanese Patent Kokai Nos. Hei 10-239586, Hei 6-148519, and 2000-193894.
In order to find the lesion as easily as possible, a capsule type endoscope that, in addition to a function of carrying out an ordinary observation through a color image, for example, is capable of irradiating a living tissue with excitation light to observe fluorescence from the living tissue is proposed. Such a capsule type endoscope is disclosed, for example, in PCT WO 02/36007. An example of a technique for making observations on both an ordinary color image and a particular image represented by a fluorescent image is disclosed in PCT WO 03/11103.
In one of the observations of the particular image used together with the ordinary color image in order to find the lesion as easily as possible, there is a technique referred to as narrow band imaging (hereinafter abbreviated to NBI) in which the living tissue is irradiated with narrow-band light and reflected light from the living tissue is imaged and observed. Its feature is as described below. For example, short-wavelength light, such as blue light, has a small penetration depth into a living body. Consequently, when short-wavelength, narrow-band light is used in the NBI, this short-wavelength light, containing only information about the surface of the living tissue, is reflected, and thus an observation image specializing the surface of the living tissue can be obtained. On the other hand, when light of a large penetration depth into the living body, such as red light, is used in the NBI, this long-wavelength light, containing information on the deep part of the living tissue, is reflected, and thus a state of the deep part of the living tissue can be imaged. In the NBI, for example, it is possible to clearly depict the capillary of the surface of a mucous membrane without spraying pigment on the surface of the living body or injecting a contrast medium, such as indocyanine green (ICG), around a tumor produced in the living tissue. Thus, in the capsule type endoscope, a combination of the observation of the ordinary color image with the NBI contributes to the improvements of accuracy of the detection of Barrett's esophagus and glandular cancer in early stages; the identification of differentiation, an invasion area, and a penetration depth of cancer detected at early stages; assistance to a pit pattern diagnosis of the tumor of the large intestine; and a stage diagnosis of a inflammatory intestinal disease. When the NBI is combined with a high-magnification endoscopic observation, a further effect is brought about.